Xcode 5 by default uses the username from OS X when committing in git. I am not sure what the default is used for the email but it's not correct. If you run a command to look at the recent logs like.
> git log -2
In my case I can see that my wife's account committed something in git and it has this funky email address.
Fixing author issues
To fix this I ran the following command from the command line
> vi .gitconfig
And place your username and email address in it
name = Patrick Bailey
email = email@example.com
And save it
Now when you commit a file in Xcode it will use the username and email from this file.
There are other default settings you can put in this file but this is enough for username and password.